Andy Pettitte smiled. It was the kind of smile that told you he was completely at peace with his decision to retire. The kind of smile that told you he is ready to move on with his life.

Pettitte had just finished talking to the media, announcing his retirement (again) and was heading through the tunnel on his way into the Yankees’ clubhouse. The left-hander had spent 25 minutes looking back and looking forward at a press conference attended by Mariano Rivera.

“I’m not going to lie to you,’’ Pettitte told The Post Friday night. “I’ve been so stressed about this announcement, I just didn’t want to take anything away from Mo, but now that it’s out, it’s like a ton, like a weight has been lifted off my shoulders. So I actually feel great about announcing it now and I thought I was going to feel terrible about it.’’

Andy, you can relax now. Your job in New York is nearly done.

All that’s really left is to officially say goodbye to the fans Sunday and finish the season. That is why Pettitte announced his retirement Friday. He wanted the fans to know this was goodbye, his endless summer of a career has finally come to an end.

“When I retired the last time I never had the chance to tell the fans,’’ Pettitte said.

Then he said these words that perfectly describe Yankees fans: “Look, they’re tough, but that kept me going, that is what pushed me all these years and it kept me humble. They drove me to try to be great. Not that I felt that I was ever great but they drove me to try to achieve. They’ve just been great to me.’’

Pettitte, 41, achieved so much. He has pitched exactly 3,300 regular-season innings, compiling a 255-152 record over 18 seasons, and another 276²/₃ innings in the postseason with a 19-11 record. Pettitte was not an ace. He was a grinder and that is what makes him so special to the fans of New York. They could relate to his work ethic.

“I gave this game everything I got,’’ Pettitte said. “I never took this game for granted. I was all in.’’

Now, he is as ready to retire as I’ve ever seen a player, ready to go back home to Texas and spend time with his wife and four children.

That is what life is about now.

Pettitte mentioned he had just one regret, the human-growth hormone episode.

“Any kids that watched me handle that situation would know that you never think that that was the right thing to do or anything like that,’’ Pettitte said, searching to find the right words. “I know in my heart and I’ll tell you, I never tried to cheat this game. I never tried to do anything to cheat this game. I never tried to cheat anything in my life. I kind of danced around that over the last five or six years, but that’s the truth. I would hate that if any young person would think that I would try and cheat this game or other players.’’

That comment also lifted a weight off Pettitte’s wide shoulders.

Pettitte said his greatest moment was “winning that first championship in ’96 because that’s what you dream of as a kid, that’s what you play for. And it was pretty special in ’09 to be able to win that championship here. The new ballpark, that first year at an age when a lot of people didn’t think we’d be able to pull it off.’’

Andy Pettitte, Mr. Clincher, pulled it off. When he became the winning pitcher in that World Series deciding game at the age of 37, his second World Series victory that October, Pettitte earned a most special place in pinstripe history.

Only time will tell if Pettitte makes the Hall of Fame, but he deserves a place in Monument Park. The lefty who officially announced his retirement Friday should someday have his number 46 retired by the Yankees.